The presence of brain associated hematopoietic antigen on cultured bone marrow cells (Dexter cultures) is being examined. Brain associated stem cell antigen and the brain associated antigen found on pre-T cells is being determined by treating the cultured cells with appropriately absorbed rabbit anti mouse brain antiserum and testing their ability to generate cfu-s or Thy 1 positive cells in response to thymopoietin. Bone marrow cells are being cultured in the presence of thymic epithelium cells and the expression of brain associated O antigen is being determined.